W. F. Bewley 117 



of temperature and lioht are favourable to the fungus, the disease 

 symptoms appear quite suddenly and the plants wilt while still green. 

 During the night the plants may recover their turgidity, only to wilt 

 again as the morning advances. The leaves wither from the base of the 

 plant upwards, adventitious roots emerge from the stem and the plant 

 dies. Death is much slower when the conditions are less favourable to 

 the fungus: yellow blotches appear on individual leaflets on the lower 

 leaves and these leaflets wither. 



11. ETIOLOGY. 



1. The Causal Organism. 



Since Massee described the disease as it existed in the British Isles 

 in 1896, no further investigations have been carried out, and his views 

 have been generally accepted in this country. He stated that the 

 pathogen possessed two stages, the diplocladium and fusarium forms, 

 produced from the same hyphae, but that only the fusarium stage was 

 able to infect the plant. The present investigation is concerned with the 

 disease of tomatoes grown under glass in the British Isles and especially 

 in the Lea Valley. It has been found that the diplocladium and fusarium 

 forms are not stages of the same fungus, but belong to different genera 

 and each can, under definite conditions, produce a wilt. 



In most cases Verticillium. alho-atrum and various species of Fusarium 

 may be found in the external growth at the base of a dead plant. A 

 white growth of Verticillium first develops but soon becomes tinged with 

 pink as it is overgrown by Fusaria. The almost constant appearance of 

 Fusarium spores in this relation led to the idea that a species of Fusarium 

 is always the cause of Sleepy Disease. During 1919-1920, 427 affected 

 plants from different parts of England, Scotland and the Channel Isles 

 were examined : 307 contained V erticilliuyn alone, 77 contained Verticil- 

 lium and either Fusarium ferruginosum or F. sclerotioides, 26 contained 

 Verticillium and F. oxysporum, while 17 contained F. lycopersici alone. 

 Fusarium lycopersici was the name given by Saccardo to a fungus which 

 he found growing on decaying tomato fruits and has been universally 

 applied to the species of Fusarium producing wilt disease of the tomato. 



F. lycopersici is of comparatively httle importance as a cause of 

 tomato wilt in England, but is very destructive in America, where it is 

 the primary cause of Sleepy Disease. Morphological and cultural studies 

 have been made by Clayton (5), Edgerton(io), Wollenweber(20, 2i) and 

 others. 



